By varying design specifications, a golf club can be tailored to have specific durability and performance characteristics. However, golf club design is a complex matter such that altering the specifications for even one component of the club (i.e., the club head, the shaft, the grip, and subcomponents thereof) directly affects the durability and performance of the club.
For example, a number of factors contribute to the maximum distance and the trajectory accuracy of a metal wood golf club. Among the factors contributing to these properties is the flexibility of the club face, the center of gravity of the club head, and the moment of inertia of the club head. In particular, a golf club head with a higher flexibility may confer a greater impact force to a golf ball, and generally drive the ball further. The flexibility of a golf club may be measured in terms of Coefficient or Restitution (COR) or Characteristic Time (CT), the measuring procedures for both of which are well known to those skilled in the art. Higher COR and/or CT values are indicative of higher flexibilities in golf club heads and, thus, longer driving potential.
However, varying the construction of a club face in an effort to achieve higher flexibility may negatively influence other characteristics of the club head as a whole and, more particularly, the maximum driving distance. Indeed, a variation to the club face construction that negatively influences the center of gravity or the moment of inertia of the club head may lessen the maximum driving distance by presenting a tendency for excessive loft and/or a tendency for a slice trajectory.
In addition, golf club heads must be strong overall to withstand the repeated impacts incurred by striking golf balls with the club head. The loading that occurs during this transient event can create a peak force of over 2,000 pounds. Thus, a major challenge to golf club manufacturers is to achieve a club face and body design that is able to resist permanent deformation or failure due to material yield or fracture. Manufacturers have attempted to address such strength requirements in hollow metal wood drivers by forming the club head from titanium. Titanium and its alloys are low density (roughly half the weight of steel, nickel and copper alloys). However, even when using titanium, a club head is typically constructed of three to four pieces welded together since each different piece (i.e., the face, the crown, the skirt, and the sole) incurs different stresses and roles during play. For example, the mechanical properties needed to produce a high COR face are not the same as the crown. As such, the manufacturing time and cost may be high and, in addition, the desire to create a low mass face without increasing stress in other areas of the club head is difficult to achieve.
Accordingly, there remains a continuing need in the art for golf club face constructions that increase the maximum COR or CT, minimize negative influences to the center of gravity and moment of inertia of the club head, reduce stress in other areas of the club head, and maximize the driving distance and trajectory accuracy. The present invention addresses such needs in both USGA-regulation conforming clubs and non-conforming recreation clubs. In particular, in one embodiment of the present invention, the club head satisfies the limitations have been placed on the maximum permissible COR and CT by the United States Golf Association (USGA) (i.e., maximum COR of 0.830 and maximum CT of 257 us). In another embodiment aspect, the club head of the invention is intended for recreational play and achieves a maximum COR and/or maximum CT that exceeds the USGA regulations.